Vapor pressure of iodine

Figure 3 shows the absorption spectrum of I2 vapor over the range of interest at the vapor pressure of iodine at 27°C, at moderate resolution and at low resolution. A low-resolution spectrum, obtained with wide slits, is preferable for this experiment, since the vibrational structure is averaged out, facilitating the determination of the absorbance at 520 mu. An even lower resolution may be entirely satisfactory for this experiment. 

One atmosphere equals the pressure at the surface of the earth that is due to the weight of the air. Pressure is often reported in units equal to the standard atmosphere. The value of this unit is 14.7 pounds per square inch. This is equal to the pressure produced by the weight of a column of mercury 760 mm high. Pressure is also reported in units equal to the weight of the corresponding column of mercury. The abbreviation mm Hg is used for mm of mercury. The vapor pressure of iodine at its melting point is 90 mm Hg, which is 90/760 atm or 0.118 atm. 

TABLE 3-1. THE VAPOR PRESSURE OF IODINE AS A FUNCTION OF TEMPERA IURF... 

Using the rough law stated in the text, estimate the vapor pressure of iodine at 0 C. The experimental value is 0,0299 mm Hg. 

Estimate the vapor pressure of iodine, in atmospheres, at 350 C. Would you consider it safe to heat a sealed glass tube filled with iodine to this temperature ... 

Now sections e and f are enclosed in separate tubular furnaces e is heated for 24 hours at 475 °C, and / for the same period at 225 °C. (The vapor pressure of iodine at this temperature is approximately 3 atm.) The apparatus Is then allowed to cool, and the unreacted iodine is sublimed out from e (which Is held at 100 °C) into f (held at room temperature). The tube is then broken, in dry... 

It has been found by experiment that the vapor pressure of crystals and liquids increases as the temperature is raised. Curves showing the vapor pressure of iodine crystals and liquid iodine are shown in Figure 2-16. 

Aqueous solutions of I3 have an intense yellow to brown color. The vapor pressure of iodine is important even when it is in solution. Over time, aqueous solutions of iodine exhibit a spontaneous decrease in their concentrations by vaporization. Iodine is freely soluble in organic solvents. As a practical consequence of these properties, tri-iodide ions are used in direct iodometric titfations rather than aqueous solutions of I2. Due to the iodine/tri-iodide equilibrium, whose formation constant is weak, I3 solutions contain more and less free iodine I2, which is more and less liberated as the titration reaction evolves further. In a first approximation, tri-iodide ion solutions behave like iodine solutions. The formation of this ion complex has two interests. On the one hand, it (apparently) increases the solubility of iodine, permitting the attainment of I2 concentrations that allow practical titrations. On the other hand, the fact that iodine is in large part under the form of the tri-iodide complex rather than under the free form somewhat precludes its vaporization. However, the latter fact remains nonnegligible. 

Contain surface-active agents that act as solubilizers and lower the vapor pressure of iodine. lodophors have a deep amber color that fades with depletion of the available iodine. They react with organic matter, but then more free iodine is released. After 16 hr, a few B. sub-tilis spores remain after treatment with 100-200 ppm Wescodyne. Wescodyne diluted 1 to 10 with 50% ethanol has been recommended as a handwashing disinfectant but it is not effective against nonlipid virus, e.g., poliovirus 1 in 20% bovine serum albumin or rabbit blood nor would it be effective against spores (no organic matter present) (496). Inactivates poliovirus 1 in rabbit blood in 2 min. Useful for spills of nonlipid (resistant) viruses, especially spills in safety cabinets (496). 

With iodine, a pure polyacetylene film is mounted in a glass vessel to which a bulb containing the halogen is attached. The iodine container is held at a fixed temperature to produce a known vapor pressure of iodine. The halogen content in the final product and, at various stages in the reaction, is determined from weight uptake and by chemical analysis [9]. 

The vapor pressure, of soHd iodine has been redetermined using the gas current method and by a static method using a flexible metallic diaphragm (27,28). The data from the gas current method are weU represented by equation 2 (27) ... 

Chlorine heptoxide is more stable than either chlorine monoxide or chlorine dioxide however, the CX C) detonates when heated or subjected to shock. It melts at —91.5°C, bods at 80°C, has a molecular weight of 182.914, a heat of vapori2ation of 34.7 kj/mol (8.29 kcal/mol), and, at 0°C, a vapor pressure of 3.2 kPa (23.7 mm Hg) and a density of 1.86 g/mL (14,15). The infrared spectmm is consistent with the stmcture O CIOCIO (16). Cl O decomposes to chlorine and oxygen at low (0.2—10.7 kPa (1.5—80 mm Hg)) pressures and in a temperature range of 100—120°C (17). It is soluble in ben2ene, slowly attacking the solvent with water to form perchloric acid it also reacts with iodine to form iodine pentoxide and explodes on contact with a flame or by percussion. Reaction with olefins yields the impact-sensitive alkyl perchlorates (18). 

At a given temperature, the pressure of iodine vapor is constant, independent of the amount of solid iodine or any other factor. The equilibrium constant expression is... 

The stiochiometry of the reaction was measured by reacting Pu metal with a THF solution of C2Rll2 in a sealed, evacuated flank. After 24 hours, volume and pressure measurements showed that 1.46 mm of gas was evolved, after correction for the vapor pressure of THF 1.54 mm of Pu was consumed, and titration of the THF filtrate found 1.8 mm of iodine. The gas composition was not determined, but assuming that the evolved gas was C H, these data indicate that the reaction is ... 

This experiment is in some respects similar to two other experiments eoneeming enthalpy changes attending phase transformations, namely, Exps. 13 and 47. However, it differs from them in that the experimental data, whieh are vapor pressures of solid iodine at several... 

The vapor pressures of lead and polonium iodides have been investigated. The metals were heated in an atmosphere of iodine in a closed system. The pressure of the products was determined by a statistical method. At less than 80 atomic percent iodine, P0I4 forms in the condensed phase. At 473°K P0I4 dissociates into P0I2. Above 80 atomic percent iodine, the condensed phase exhibits the presence of Pole. The enthalpy of evaporation of Pole is 116kj mole. These experiments suggest that the separation of polonium from lead can be accomplished by their volatization in iodine vapors at elevated temperatures. 

The vapor pressures of iodides of polonium were measured in a closed system. Metalhc polonium was heated in iodine vapor and the pressures were measured. At iodine concentrations below 80 atomic percent and with increasing temperatures, polonium tetraiodide is formed in the condensed phase. The tetraiodide dissociates into P0I2 beginning at a temperature of 473 °K. The evaporation enthalpy of P0I2 is 94.4kj mole. At 80 atomic percent the condensed phase exhibits the presence of Pole. 

The Vapor Pressure of a Crystal. A crystal of iodine in an evacu kted vessel will gTadually change into iodine gas by the evapoiation of molecules from its surface. Occasionally one of these free gas molecules will again strike the surface of the crystal, and it may stick to the surface, held by the van der Waals attraction of the other crystal molecules. This is called condensation of the gas molecules. 

The vapor pressure of every crystal increases with increase in temperature. For iodine it has the value 0.20 mm of mercury at... 

The vapor pressure of liquid iodine at its freezing point, 114° C, is 90 mm Hg. This is exactly the same as the vapor pressure of the crystals at this temperature, as described in the section before the preceding one. That is, iodine gas at a pressure of 90 mm Hg is in equilibrium with the liquid at 114° C, the freezing point of the liquid, and this gas is also in equilibrium with iodine crystals at this temperature, their melting point. The crystals and the liquid are in equi librium at the freezing point (melting point), and they then have exactly the same vapor pressure. If the two phases had different vapor pressures the phase with the larger vapor pressure would continue to evaporate, and the vapor would continue to condense at the other phase, until the first phase had disappeared. 

The vapor pressure of liquid iodine reaches I atm at 184° C, which is the boiling point of iodine. 

TEMPERATURE VAPOR PRESSURE Oi IODINE c r stals TEv/fpKRAI URF VAPOR PRESSURE OF LIQUID IODINE... 

FIG. 3-16. A graph showing the vapor-pressure curve of iodine crystal and the vapor-pressure curve of liquid iodine. The melting point of die crystal is the temperature at which the crystal and the liquid have the same vapor pressure, and the boiling point of the liquid (at I atm pressure) is the temperature at which the vapor pressure of the liquid equals 1 atm. 

The solubility of chlorine per 100 cc. of water at 20° is 1.85 g. that of bromine is 3.58 g. and that of iodine 0.28 g. Both chlorine and bromine form crystalline hydrates, C12-8H20 and BrjTOHjO. They are stable only at low temperatures (0-9°). The increased solubility of bromine in potassium bromide solution is ascribed to the formation of KBr if such solutions are saturated with bromine, the vapor pressure of the latter is the same as that of a water solution saturated with bromine. However, the halogen can be removed completely by extraction with carbon disulfide or by a stream of air the KBra must be stable only in the presence of free bromine. The solubility of iodine in water is increased by potassium iodide to 1.4 g. per 100 cc. and in ethanol a 20% solution can be formed. 

Pressure of iodine vapor, mm. Hg. Temperature of system, ° C. Detector... 

The variation of the vapor pressure of solid iodine is given by... 

Figure 13-16 Sublimation can be used to purify volatile solids. The high vapor pressure of the solid substance causes it to sublime when heated. Crystals of purified substance are formed when the vapor is deposited to form solid on the cooler (upper) portion of the apparatus. Iodine, fy, sublimes readily, fy vapor is purple.

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